1. Field of the Invention
The present invention relates to an image capturing apparatus for palm authentication for image capturing a palm, a portion of a human body for use in personal authentication, and more particularly an image capturing apparatus for palm authentication by correctly image capturing a palm even of an unaccustomed user, and easily extracting palm characteristics.
2. Description of the Related Art
There are many portions in a human body by which each person can be identified, such as fingerprint, retina, face and blood vessel. With the technological development in biometrics, a variety of apparatuses have been provided for personal authentication by recognizing the characteristics of the human body portions. Among them, the vessel of a palm or a palm pattern is suitable in view of reliability in the personal authentication, because a large amount of personal characteristics data is obtainable.
In particular, it is known that the vessel (vein) pattern in each person does not change throughout his or her life from a stage of fetus, and that no individuals in the world have an equal pattern. Accordingly, the vessel pattern can suitably be used for personal authentication. FIGS. 20 through 23 show explanation diagrams of the conventional palm authentication technique. As shown in FIG. 20, at the time of registration or authentication, a user puts a palm of his hand 110 near an image capturing apparatus 100. The image capturing apparatus 100 emits near infrared radiation to irradiate on the palm of hand 110. The image capturing apparatus 100 then receives the near infrared reflected from the palm of hand 110 using a sensor.
As shown in FIG. 21, hemoglobin in an erythrocyte flowing in a vein 112 loses oxygen. This hemoglobin (reduced hemoglobin) absorbs near infrared light having a wavelength near 760 nm. Therefore, when the near infrared is irradiated on the palm, only portions in which the veins exist produce small reflection of the near infrared, and accordingly, by detecting the strength of the reflected near infrared, the vein positions can be recognized.
A method for the personal authentication using a user's palm is disclosed in the official gazette of the Japanese Unexamined Patent Publication No. 2004-062826. According to the above disclosure, as shown in FIGS. 22 and 23, the user first registers the vein image data of his palm into a server or a card, using the image capturing apparatus 100 shown in FIG. 20. Next, to perform the personal authentication, the user makes the vein image data of his palm read in, using image capturing apparatus 100 shown in FIG. 20.
The personal authentication is carried out by collating the vein patterns between the registered vein image read out by a user's ID and the vein image read in for collation. For example, as a result of the collation of the vein pattern between the registered image and the collation image as shown in FIG. 22, the individual concerned is decided as being authenticated. Meanwhile, as a result of the collation of the vein pattern between the registered image and the collation image as shown in FIG. 23, the individual is decided as being not authenticated.
This authentication technique using the palm enables non-contact image capturing, which makes the user easy to use. However, the position, size and inclination of the image at the time of registration or collation become key issues. Namely, when the user places his palm above the image capturing apparatus, if there are differences in the posture, the distance between the image capturing apparatus and the palm, the position, the inclination or the size, a large difference may be produced for an identical palm between the registered image and the collation image, making it difficult to obtain an accurate collation.
Because the above difference becomes a factor of incorrect decision, the prior art has proposed provision of an image processing function and a sensor for guiding a palm to an image capturing range of the image capturing apparatus. However, the above disclosed guidance method is effective for users who are accustomed to such an apparatus. When the apparatus aims at unaccustomed users also, the above method is not convenient, particularly when the users want to register for the first time, or when the users have relatively little knowledge of the apparatus.
This may prevent the apparatus from ubiquitous application to come, for use in anytime, anywhere, and by anyone. Furthermore, if the operation is time-consuming, widespread use of the apparatus may be impeded from the standpoint of users and the apparatus manufacturer.